High-Field EPR Spectroscopy on Proteins and their Model Systems

2008 ◽  
Keyword(s):  
Epr Spectroscopy ◽  
High Field ◽  
Model Systems

scholarly journals Biomolecular EPR Meets NMR at High Magnetic Fields

2018 ◽  
Vol 4 (4) ◽  
pp. 50 ◽  
Author(s):  
Klaus Möbius ◽  
Wolfgang Lubitz ◽  
Nicholas Cox ◽  
Anton Savitsky
Keyword(s):  
Solid State ◽  
Transition Metal ◽  
Epr Spectroscopy ◽  
High Field ◽  
Double Resonance ◽  
Reaction Centers ◽  
Photosynthetic Reaction Centers ◽  
Reaction Intermediates ◽  
Frozen Solution ◽  
Epr Experiments

In this review on advanced biomolecular EPR spectroscopy, which addresses both the EPR and NMR communities, considerable emphasis is put on delineating the complementarity of NMR and EPR regarding the measurement of interactions and dynamics of large molecules embedded in fluid-solution or solid-state environments. Our focus is on the characterization of protein structure, dynamics and interactions, using sophisticated EPR spectroscopy methods. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultrafast electronics for signal data handling and processing have pushed the limits of EPR spectroscopy to new horizons reaching millimeter and sub-millimeter wavelengths and 15 T Zeeman fields. Expanding traditional applications to paramagnetic systems, spin-labeling of biomolecules has become a mainstream multifrequency approach in EPR spectroscopy. In the high-frequency/high-field EPR region, sub-micromolar concentrations of nitroxide spin-labeled molecules are now sufficient to characterize reaction intermediates of complex biomolecular processes. This offers promising analytical applications in biochemistry and molecular biology where sample material is often difficult to prepare in sufficient concentration for NMR characterization. For multifrequency EPR experiments on frozen solutions typical sample volumes are of the order of 250 μL (S-band), 150 μL (X-band), 10 μL (Q-band) and 1 μL (W-band). These are orders of magnitude smaller than the sample volumes required for modern liquid- or solid-state NMR spectroscopy. An important additional advantage of EPR over NMR is the ability to detect and characterize even short-lived paramagnetic reaction intermediates (down to a lifetime of a few ns). Electron–nuclear and electron–electron double-resonance techniques such as electron–nuclear double resonance (ENDOR), ELDOR-detected NMR, PELDOR (DEER) further improve the spectroscopic selectivity for the various magnetic interactions and their evolution in the frequency and time domains. PELDOR techniques applied to frozen-solution samples of doubly spin-labeled proteins allow for molecular distance measurements ranging up to about 100 Å. For disordered frozen-solution samples high-field EPR spectroscopy allows greatly improved orientational selection of the molecules within the laboratory axes reference system by means of the anisotropic electron Zeeman interaction. Single-crystal resolution is approached at the canonical g-tensor orientations—even for molecules with very small g-anisotropies. Unique structural, functional, and dynamic information about molecular systems is thus revealed that can hardly be obtained by other analytical techniques. On the other hand, the limitation to systems with unpaired electrons means that EPR is less widely used than NMR. However, this limitation also means that EPR offers greater specificity, since ordinary chemical solvents and matrices do not give rise to EPR in contrast to NMR spectra. Thus, multifrequency EPR spectroscopy plays an important role in better understanding paramagnetic species such as organic and inorganic radicals, transition metal complexes as found in many catalysts or metalloenzymes, transient species such as light-generated spin-correlated radical pairs and triplets occurring in protein complexes of photosynthetic reaction centers, electron-transfer relays, etc. Special attention is drawn to high-field EPR experiments on photosynthetic reaction centers embedded in specific sugar matrices that enable organisms to survive extreme dryness and heat stress by adopting an anhydrobiotic state. After a more general overview on methods and applications of advanced multifrequency EPR spectroscopy, a few representative examples are reviewed to some detail in two Case Studies: (I) High-field ELDOR-detected NMR (EDNMR) as a general method for electron–nuclear hyperfine spectroscopy of nitroxide radical and transition metal containing systems; (II) High-field ENDOR and EDNMR studies of the Oxygen Evolving Complex (OEC) in Photosystem II, which performs water oxidation in photosynthesis, i.e., the light-driven splitting of water into its elemental constituents, which is one of the most important chemical reactions on Earth.

scholarly journals High-Field Pulsed ENDOR with Intra-cavity Radiofrequency Coil

2020 ◽  
Vol 51 (11) ◽  
pp. 1433-1449
Author(s):  
G. Annino ◽  
H. Moons ◽  
M. Fittipaldi ◽  
S. Van Doorslaer ◽  
E. Goovaerts
Keyword(s):  
Magnetic Field ◽  
High Field ◽  
Conversion Factor ◽  
Signal To Noise Ratio ◽  
Model Systems ◽  
Signal To Noise ◽  
Radiofrequency Coil ◽  
W Band ◽  
Radiofrequency Current ◽  
Field Uniformity

AbstractThis study compares the performance of two coil configurations for W-band pulsed ENDOR using a setup with both a radiofrequency ‘hairpin’ coil internal to a microwave non-radiative resonator and Helmholtz-like coils external to the resonator. Evaluation of the different coil performances is achieved via the ENDOR study of two model systems. The efficiencies of the coil configurations are first investigated numerically, showing that a higher radiofrequency current-to-magnetic field conversion factor can be achieved with the intra-cavity coil, with a similar radiofrequency magnetic field uniformity. This result is then confirmed by the broadband ENDOR spectra acquired with the two coil arrangements. A gain in the signal-to-noise ratio enabled by the internal coil of about a factor 10 was observed. In some cases, the high conversion factor of the intra-cavity coil led to a saturation of the ENDOR transitions. The possibility to implement a similar intra-cavity radiofrequency coil configuration in higher field spectrometers is finally discussed.

EPR Spectra from “EPR-Silent” Species:  High-Frequency and High-Field EPR Spectroscopy of Pseudotetrahedral Complexes of Nickel(II)

2002 ◽  
Vol 41 (17) ◽  
pp. 4478-4487 ◽  
Author(s):  
J. Krzystek ◽  
Ju-Hyun Park ◽  
Mark W. Meisel ◽  
Michael A. Hitchman ◽  
Horst Stratemeier ◽  
...  
Keyword(s):  
Epr Spectroscopy ◽  
High Frequency ◽  
High Field ◽  
Epr Spectra

Cation and Water Interactions in the Interlamellae of a Smectite Clay

1997 ◽  
Author(s):  
Andrea Labouriau ◽  
Cliff T. Johnston
Keyword(s):  
Nmr Spectroscopy ◽  
High Field ◽  
Model Systems ◽  
Strong Interactions ◽  
Chemical Information ◽  
Nmr Studies ◽  
Humic Materials ◽  
Structural Metals ◽  
And Diffusion

Advances in NMR instrumentation and availability have led to increased application to mineral systems and to environmental problems. The sensitivity of high-field NMR systems is nearly sufficient to work at real environmental concentrations. Even with limited sensitivity, the amount of chemical information obtained through NMR spectroscopy makes it a very valuable technique in many model systems. The application of NMR spectroscopy in mineral systems has been primarily limited to studies of the structural metals aluminum and silicon. However, in recent years there have been several publications on mobile cations in minerals, including work on the exchangeable cations in clays. Our interests lie in understanding the sorption of cations in clays, the structural sites available for that sorption, and the role of water in cation–clay interactions. Our goal is to eventually understand the molecular interactions that determine the adsorption and diffusion of cations in clays and, thus, the role of clays in determining cation transport through the geosphere. This fundamental understanding has applications in the fate of heavy metals, radionuclides, and even the mobility of nutrients for plants. It is well known that there are very strong interactions between metals and humic materials and these are also strong contributors to cation mobility. However, for simplicity, we have chosen to focus on the interactions of mobile metal ions with well-characterized clays. An NMR-based approach to this problem can take two complementary directions: first, studies of the structural components of clays such as 29Si and 27Al NMR as a function of cation or hydration; second, NMR studies of probe molecules—which in this case are the cations themselves. High magnetic field, multinuclear NMR spectrometers make it quite possible to study various “uncommon” nuclei with relative ease. It is our experience that using the cations as probe nuclei for studying sorption phenomena yields more information than studies of structural nuclei. This chapter is basically a report of work in progress on several systems that are starting to yield interesting results, which it is hoped will lead to a general understanding of these complex systems.

Dynamics in the Mn2+Binding Site in Single Crystals of Concanavalin A Revealed by High-Field EPR Spectroscopy†

Biochemistry ◽  
2003 ◽  
Vol 42 (25) ◽  
pp. 7863-7870 ◽  
Author(s):  
Raanan Carmieli ◽  
Palanichamy Manikandan ◽  
Boris Epel ◽  
A. Joseph Kalb (Gilbo ◽  
Alexander Schnegg ◽  
...  
Keyword(s):  
Binding Site ◽  
Single Crystals ◽  
Concanavalin A ◽  
Epr Spectroscopy ◽  
High Field
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